Chert fragments

Sihceous matter other than clay may occur in the free state as sand, quartz fragments, and chert, and in the combined state as feldspar, mica, talc (qv), and serpentine. Metallurgical and chemical limestones should contain less than 1% alumina and 2% siUca. 

Calcite-cemented fill (Fb) calcite-cemented breakdown or calcite-coated floor angular to subangular fragments of limestone and chert up to cobblesized calcite-coated bedrock or other cave fill. 

Volcanic rock fragments of intermediate composition are generally the most abundant lithic fragments, averaging 70-90% of all rock fragments (Fig. 5). Chert is the most common sedimentary rock fragment, although some units contain abun-... 

A few thin lenses of tight, gray, plastic clay also occur in the residuum beneath the study field. The clay is dense and contains small fragments of chert and silicified limestone. The maximum observed thickness of the clay lenses is 5 ft in the southeastern corner of the field. Although they are areally restricted, the clay lenses act as semiconfining zones. 

Twenty samples of cherts from the Central Pacific were selected for analysis. Of those, 18 are in stratigraphic sequence from DSDP Hole 167 (Leg 17). Hole 167 was drilled atop the Magellan Rise in the Central Pacific. It penetrated about 1200 m of nanofossil chalk, limestones and cherts, Tithonian to Pleistocene in age. Starting with core 33, at a depth of 605 m below sea floor (mbsf), cherts were recovered in the sequence. The cherts occur either as part of the carbonate sequence or, very often as broken fragments in the core catcher (marked cc in Table 1). 

Sand and sandstone are assemblages of quartz, chert, feldspar, mica, fragments of feldspar-rich igneous, sedimentary, and metamorphic rocks, fossils, clay, and other constituents in various percentages. Sandstones contain cements, normally calcite or quartz, or a clay matrix, that bind the grains together. These rocks, therefore, typically contain a mixture of monocrystalline and polycrystalline particles. 

The phosphorites consist of carbonate-fluorapatite mixed with varying amounts of quartz silt, clay minerals, calcite, dolomite, chert and carbonaceous matter. Most of the phosphate occurs as pellets with amounts of oolites, intraclasts, scales, phosphatic shells and replaced skeletal grains. The pellets are cemented with dolomite, calcite, phosphate or, rarely, chert. Some phosphorite beds are composed of phosphate mud. There is a general decrease in size and abundance of intraclast fragments and an increase in carbonaceous content in the phosphorite beds toward the west. These characteristics, plus the close association of phosphorites with cherts and... 

Hence, the Edvrards (GC) rock consists mainly of macropores. In contrast, the Fort Riley carbonate is characterized by about an eight times higher fraction of micro- and mesopores than the Edwards (GC). Berea sandstone C3 exhibits the largest fraction of micro- and mesopores (over S %), which is about twice as much as for the Berea sandstone PH2. In Berea sandstone, chert, lithic fragments, partially dissolved feldspars, sheet pores at crystal boundaries and clays contribute to microporosity. 

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